1. Field of the Invention
The present invention relates to a one-way clutch. This one-way clutch is mounted not only in feed mechanisms for a variety of functional apparatus but also in a pulley belonging to an accessory to be driven through a belt by the crankshaft of an engine of an automobile or the like. This accessory is exemplified by an air conditioner compressor, a water pump, alternator or a cooling fan for the automobile.
2. Description of the Related Art
The one-way clutch is constructed to have two annuli of different diameters (of which the diametrically smaller annulus is an inner annulus whereas the diametrically larger annulus is an outer annulus) arranged concentrically and is interchanged between a locked state, in which the rotating power is transmitted from one annulus to the other, and a free state in which the power transmission is interrupted. A one-way clutch for establishing such locked and free states, wedge-shaped spaces are formed at a plurality of circumferential portions in a radially facing space between the two annuli, and rollers as wedge members are arranged in the wedge-shaped spaces. These wedge-shaped spaces are formed between the cylindrical outer circumference of the inner annulus and the radially outward recessed faces (or cam faces) formed at a plurality of circumferential portions of the inner circumference of the outer annulus.
It has been discovered by us that the one-way clutch having the cam faces on the inner circumference of the outer annulus has a tendency to have the wedge actions weakened at the locked time of the rollers in a high-speed range in which the centrifugal force rises. More specifically, the turning actions of the rollers to the locked position or the free position are guided such that the rollers are pushed onto the cam faces of the outer annulus by the centrifugal force. The centrifugal force acts, in its rising situation, to bring the rollers toward the radially larger sides of the cam faces, i.e., toward the free position. As a result, the delay angle (i.e., the angle made among the locked position, the free position and the turning center) has a tendency to grow more than necessary to delay the locking action.
From this, we have proposed a one-way clutch which has cam faces on the outer circumference of the inner annulus. In this one-way clutch, the inner circumference of the outer annulus for guiding the rollers is made cylindrical to have a constant internal diameter at the individual circumferential portions of the one-way clutch, so that the centrifugal force to act upon the rollers does not act as a force to turn the rollers in the circumferential direction. In short, the wedge actions of the rollers are not weakened by the centrifugal force.
The inner annulus in the one-way clutch, as proposed by us, is shaped in its contour by a machining treatment and is enhanced in its surface hardness by a hardening treatment such as a high-frequency hardening treatment and in its facial accuracy especially of the cam face regions by a polishing treatment. The hardening treatment of this case is performed by the high-frequency hardening treatment so that a strain occurs in the surface of the inner annulus after the hardening treatment. Thus, the facial accuracy is retained by the aforementioned polishing treatment.
However, this working treatment takes troubles to raise the cost for manufacturing the one-way clutch.